1. Field of the Invention
The present invention relates to an ink jet recording apparatus such as a printer mountable on or connectable to a copying machine, communication equipment or information equipment, and a method for recovering a recording head used with such equipment. More particularly, the present invention relates to a positive recovery mechanism for systems each having a heat generating element for forming a bubble in ink by generating thermal energy, and a drive circuit for driving such heat generating element by an electric pulse signal.
2. Related Background Art
As disclosed in U.S. Pat. No. 4,740,796 and West German Public Disclosure No. 2843064,fundamental inventions for generating bubbles by utilizing thermal energy are embodied as apparatus wherein heat generating resistance elements are driven by electric pulse signals, or apparatus utilizing optical energy. Further, apparatus having conversion elements for converting optical energy into thermal energy are already known.
In the ink jet recording field, other than a recording operation, a recovery operation, referred to as preliminary discharge, for discharging ink from discharge openings has been performed. A technique in which the preliminary discharge is effected at the proper timing during the recording operation or during a waiting condition is also known, as disclosed in Great Britain Patent No. 2169855. This patent specification concretely discloses the recovery operation effected as the preliminary discharge during the normal recording operation.
On the other hand, a recovery operation using a pump, normally referred to as absorb recovery, for recovering an extremely jammed recording head has been practically used. Also in U.S. Pat. No. 4,977,459 wherein the fact that a proper recovery treatment is effected in accordance with a condition of a recording head is disclosed, the final positive recovery treatment is performed by the absorb recovery, rather than by the preliminary discharge.
Further, since the conventional preliminary discharge was frequently carried out, the discharge condition for the preliminary discharge was the same as or similar to the discharge condition for the normal recording operation, in order to extend the service life of heat generating elements of the recording head. The ink discharged by the preliminary discharge is normally directed to an ink absorber; however, other than the ink absorber, it is known to use an exclusive paper sheet, a recording sheet, a foam body or a cap for capping the recording head as an ink receiving member.
Furthermore, in order to improve the recovery effect of the preliminary discharge, an epochal invention wherein the absorb recovery while closely contacting with a recording head is used together with the preliminary discharge has been proposed, as described in U.S. patent application Ser. No. 198,733 filed on May 25, 1988 by assignee of the application now U.S. Pat. No. 5,298,923.
On the other hand, a technique referred to as idle absorb in which, after the absorb is effected while a cap is being closely contacted with a recording head, the interior of the cap is communicated with the atmosphere before the cap is separated from the recording head, or the suction of the interior of the cap is effected after the cap is separated from the recording head is disclosed in U.S. Pat. No. 4,967,204. An object of this patent is to prevent the leakage of ink from the cap.
By the way, in an invention described in U.S. patent application Ser. No. 745,480 now U.S. Pat. No. 5,289,207 which was filed on Aug. 14, 1991 by assignee of this application prior to the priority date (Oct. 18, 1991) of this application, there has been proposed a recovery treatment which can solve problems regarding the adhesion of foreign matters to discharge elements of thermal energy generating type for a long term non-operation of the recording head and/or the variation in the fluidity of ink due to the difference in the frequency of use of individual discharge openings. A typical embodiment of the invention relates to a recovery method wherein the ink is discharged onto a recording medium or into a cap and which includes a positive recovery mode for effecting 10.sup.3 or more preliminary discharges by supplying the energy smaller than the minimum energy E.sub.0 required to generate the film boiling and greater than the energy required to effect the normal discharge.
The inventors of this invention aimed or assumed to eliminate the waste of the recording media in carrying out the positive recovery mode in the above-mentioned recovery method. Now, since it was found that there was a great amount of discharged ink and the discharged ink was rebounded, the cap was closely contacted with the recording head during the preliminary discharge. However, when done, the surface of the recording head was covered by large amount of ink. As a result, it was impossible to discharge the ink stably, and further, it was difficult to clean the surface of the recording head (that is, the ink could not be removed from the surface of the recording head completely by the normal cleaning method, thus still remaining the ink on the head surface). When the recording operation was effected in this condition, the recording ink discharges were distorted or disordered. Accordingly, in the aimed arrangement, although the recovery of the interior (discharge openings) of the recording head could be attained, a new problem regarding the recovery of the surface of the recording head arose, and thus, the satisfactory recovery effect could not be achieved.
Further, it was found that, when the above-mentioned positive recovery mode was effected by a color recording means, a large amount of ink exceeding the ink absorbing ability of the recording medium was discharged, thus causing the contamination of internal parts of the recording apparatus due to the poor fixing and/or the mixing of colors during the cleaning operation by a cleaning blade.
From another point of view, the inventors found that the ability for receiving a large amount of ink from the preliminary discharge was reduced due to the change in position of the cap, thus causing a problem regarding the leakage of ink.